It is conjectured that every positive integer may be
written as the sum of seven nonnegative cubes except these
seventeen: {15, 22, 23, 50, 114, 167, 175, 186, 212, 231,
238, 239, 303, 364, 420, 428, 454}. This conjecture has
been tested to 1034 and proven for numbers
divisible by four. [Caldwell]